Many critical safety and environmental applications require monitoring not only of one gas concentration, but of several gases. For example, the air control equipment in mines has to control the methane concentration and also the concentration of oxygen, and it is therefore necessary to monitor both the concentration of methane and that of oxygen in the mine atmosphere. Conventional equipment comprises a set of the required sensors, usually different types for different gases (e.g. catalytic for methane, electrochemical for oxygen, etc). The recent major tendency in the gas analysis industry is a transition towards optical sensors since these are generally believed to be the most accurate and reliable. The most developed optical technology for gas analysis is nondispersive infrared (NDIR) technology, but at present this cannot be utilized for the whole range of gases required by industry (for instance, there is no NDIR sensor for oxygen). Nevertheless, other optical technologies could be used to cover the shortage for the multi-gas optical sensors.